1. Field of the Invention
The present invention relates to a method of mounting a lead wire on a titanium member, an electrode having a lead wire mounted thereon by the method, and a spot welder used for manufacturing the electrode.
2. Related Art
Stainless steel, for example, has hitherto been used as an electrode element for a biomedical electrode to be used for electrically stimulating a living body from a body surface.
However, when stainless steel is used as an electrode element for electrical simulation, the following problems arise.
(1) Corrosion arises in an electrode element as a result of energization, thereby inducing dissolve of ions, such as iron ions, nickel ions, and chromium ions. As a result, the electrode element undergoes reduction in strength and deterioration in appearance.
(2) The thus-dissolved ions (particularly nickel ions and chromium ions) induce contact dermatitis or an allergic reaction.
On the contrast, if noble metal, such as gold or platinum, is used for an electrode element, dissolve of ions can be retarded. However, these substances are expensive and inappropriate for employment of high purity materials for common applications, such as a biomedical electrode.
For this reason, under another conceivable method a stainless steel electrode element is plated with gold or the like, thereby preventing dissolve of ions from the surface of the electrode element and curtailing costs. However, pits or pin holes or loss of a plating layer due to a deficiency in mechanical strength results in exposure of stainless steel, thus causing dissolve of ions by a galvanic current.
These problems have been known to be solved by use of titanium as material for the electrode element (as described in Published Japanese translation of a PCT patent publication No. 501816/1984, WO84/01298).
Titanium resists corrosion. Even when electric current is applied to titanium immersed in saline solution, a considerably small amount of ions are dissolved. For this reason, even if titanium is used as an electrode element of a biomedical electrode, it won't cause reduction in strength of the electrode or surface deterioration of the electrode.
Further, titanium is less toxic. Even if ions are dissolved, the ions will not induce contact dermatitis, poisoning, or allergic reaction. Hence, titanium is safe.
Titanium is also less expensive than gold or platinum and can be used as high-purity material for a biomedical electrode.
In contrast with stainless steel or gold, titanium cannot be soldered. Hence, when titanium is used as an electrode element, difficulty is encountered in attaching a lead wire to the electrode element. For this reason, no electrode structure in which a lead wire is readily attached to a titanium electrode element has hitherto been available, and an attachment method is complicated (as described in Examined Japanese Patent Publication No. 45622/1981 and U.S. Pat. No. 3,749,101).